The optical transitions in 20 nm wide silicon and beryllium δ -doped GaAs/AlAs multiple quantum wells with various doping levels were investigated at different excitation intensities. A fractional dimensionality model was used to describe the free hole-donor and free electron-acceptor transitions in the quantum wells. The measured photoluminescence spectra from samples of different doping level related to donor-impurity or acceptor-impurity induced effects in the photoluminescence lineshape, were compared within the framework of these model calculations. Both experimentally and theoretically it was shown that acceptor and donor related optical transitions and photoluminescence line shapes were related to the difference in the effective masses of holes and electrons. This effect also leads to a difference in the photoluminescence spectra in which the luminescence band for the donor related spectrum is narrower in comparison to the acceptor related spectrum.